GO is basically a student extracurricular head. In different schools it takes different means to become GO. Sometimes, it means that your fellow students picked you to run for GO, which means you’re popular amongst the student-folk. Sometimes, the faculty picks a girl as GO, no campaigning involved. That means that the faculty loves you. 🙂
And yes, in most schools, it means how much class can you and the rest of the school miss. This being the case, a GO head is usually a good, intelligent student, who can keep up with the work regardless of how many hours of class she has missed. Two of my sisters were GO heads. And yes, they are both great, wonderful people. (But so am I, and I wasn’t GO. LOL)